This invention relates to fluid motor-pump units. More specifically, this invention relates to an improved hydraulic fluid motor-pump unit having a dynamically pressure-balanced rotating valve plate.
In the prior art, a wide variety of motors, pumps, and other power transfer devices are known for handling fluids such as hydraulic liquids. These devices include, but are not limited to, gear pumps, vane-type pumps, and positive displacement piston pumps such as so-called swash plate pumps. In many applications, positive displacement swash plate pumps are preferred, and include a circumferentially arranged set of axially oriented pistons reciprocally driven to move fluid between high and low pressure hydraulic ports. See, for example, U.S. Pat. Nos. 2,762,307; 2,876,704; 3,613,511; and 4,095,421. These piston pumps are desirable because of their relatively rapid responsiveness and high efficiency at relatively high pumping speeds and pressures, making them particularly suited for use with modern aerospace hydraulic systems. Of course, these devices are usable in either a motor or pump mode, depending upon whether power is being transferred to or from the hydraulic system.
In typical prior art swash plate piston pumps, the circumferentially arranged pistons are received in a matingly configured cylinder block with a valve plate interposed between the cylinder block, and the high and low pressure hydraulic ports. In operation, either the valve plate or the cylinder block wth pistons must be rotated to sequentially port the fluid transferred by the reciprocating pistons between the high and low pressure ports. See U.S. Pat. Nos. 2,661,701; 2,876,704; 3,073,254; 3,238,888; 3,747,476 and 4,095,921 for examples of units with rotating cylinder blocks and stationary valve plates, and U.S. Pat. Nos. 2,762,307 and 3,613,511 for examples of units with stationary cylinder blocks and rotating valve plates.
These prior art swash plate piston pumps include inherent design limitations which limit the efficiency and speed range of the pumps, and thereby also limits their utility. For example, in units having a rotating cylinder block, substantial energy is required to overcome internal friction in order for the components to rotate, particularly upon start-up of the unit. Moreover, centrifugal forces and force imbalances resulting from rotation of the reciprocating pistons further increases internal pump friction and vibrations. These frictional and vibrational factors all contribute to limit undesirably the efficiency and speed range of the unit.
Another inherent design problem relates to the provision of a satisfactory seal between the valve plate and the cylinder block, regardless of which component is rotating. That is, relative rotation between the valve plate and the cylinder block must be relatively leak-free to prevent losses in efficiency, but still guard against excessive friction or wear between the components. However, sealing concepts in the prior art typically have used simple seal rings or gaskets which are not satisfactorily wear-resistant, or clamping springs which supply relatively large spring forces for urging the cylinder block and valve plate into sealing alignment. Such clamping springs contribute to high component wear, as well as to increased internal pump friction to substantially decrease operating range.
Some attempts have been made to statically pressure-balance a nonrotating valve plate of a piston pump in order to provide a leak-free and relatively low friction seal between the valve plate and the cylinder block, and thereby eliminate the use of large clamping springs. Specifically, these designs comprise the provision of axial valve plate openings, and pressure-balancing pistons for equalizing fluid pressures on opposite sides of the stationary valve plate. However, static pressure-balancing techniques are limited to use with nonrotating valve plates. Accordingly, the pressure-balanced plate is necessarily aligned with a rotating cylinder block and pistons which includes the substantial friction and efficiency losses described above due to cylinder block and piston rotation.
In some applications, it is desirable to transfer power from one hydraulic system to another. This is particularly true with aircraft control systems, such as flap actuator systems, wherein alternate and/or standby hydraulic control power is required. Positive displacement swash plate piston pumps have been used in power transfer units by connecting two pump units back-to-back with aligned and connected sets of pistons. One of the pumps is hydraulically operated in a motor mode to drive the other pump in a pump mode, and thereby transfer power from one hydraulic system to another. Some of these power transfer units have been designed with back-to-back rotating cylinder blocks, and thus include relatively high internal friction and efficiency losses resulting from cylinder block and piston rotation. See, for example, U.S. Pat. No. 1,019,521. Other designs utilize stationary cylinder blocks and rotating valve plates, such as those shown in U.S. Pat. Nos. 2,845,030 and U.S. Pat. No. 15,756. However, none of these prior art power transfer unit designs have overcome the problem of providing an adequate seal between valve plates and cylinder blocks without rapid or high wear, or without the use of relatively large clamping forces.
The fluid motor-pump unit of this invention overcomes the problems and disadvantages of the prior art by providing an improved power transfer unit having a stationary cylinder block and a rotating valve plate, wherein the rotating valve plate is dynamically pressure-balanced for relatively low friction, low wear, and minimum leakage operation.